1. Field of the Invention
The invention relates generally to the field of direct-to-digital holography (interferometry). More particularly, the invention relates to reduction of direct-to-digital holography reference hologram noise and/or reduction of direct-to-digital holography Fourier space smearing.
2. Discussion of the Related Art
Prior art direct-to-digital holography (DDH), sometimes called direct-to-digital interferometry, is known to those skilled in the art(1-3). For instance, FIG. 1 illustrates one simplified embodiment of a DDH system. Light from a laser source 105 is expanded by a beam expander/spatial filter 110 and then travels through a lens 115. Subsequently, the expanded filtered light travels to a beamsplitter 120. The beamsplitter 120 may be partially reflective. The portion of light reflected from the beamsplitter 120 constitutes an object beam 125 that travels to the object 130. The portion of the object beam 125 is that is reflected by the object 130 then passes through the beamsplitter 120 and travels to a focusing lens 145. This light then passes through the focusing lens 145 and travels to a charge coupled device (CCD) camera (not shown).
The portion of the light from the lens 115 that passes through the beamsplitter 120 constitutes a reference beam 135. The reference beam 135 is reflected from a mirror 140 at a small angle. The reflected reference beam 135 from the mirror then travels toward the beamsplitter 120. The portion of the reference beam 135 that is reflected from the beamsplitter 120 then travels through the focusing lens 145 and toward the CCD camera (not shown). The object beam 125 from the focusing lens 145 and the reference beam 135 from the focusing lens 145 constitute a plurality of object and reference waves 150 and will interfere at the CCD to produce the interference pattern characteristic of a hologram as noted in U.S. Pat. No. 6,078,392.
A limitation of this technology has been reference hologram noise and/or smearing in Fourier space. What is needed, therefore, is a direct-to-digital holography approach that reduces reference hologram noise and/or Fourier space smearing.